Right now, I think the best would be:
David Lapham - Stray Bullets had been in my Top 10 Comics Ever list for a while and its return is like there had never been any decade-long hiatus. It’s seriously amazing.
Jason Aaron - For the reasons everyone’s already got.
Jonathan Hickman - Currently putting out one of my favorite comics, East of West. I haven’t liked the other stuff I’ve read by him, but those were all from when he was just starting out. That East of West is so good earns him this spot.
Greg Rucka - The master of world-building and political intrigue/commentary. Lazarus is, at this point, close to being better than Queen & Country, if not already there.
Kelly Sue DeConnick - Pretty Deadly is some impressive, heady stuff. Creating its own mythology.
Emily Carroll - It’s hard to make horror comics. She does it very well. The longest, final story in her recent Through the Woods collection will make it hard to feel safe in your own skin once you put the book down.
Jesse Moynihan - World-building, mysticism, imagination, humor, gods who talk like bros. All that and more in Forming. He’s also a major creative force in Adventure Time.
Jeff Lemire - Trillium and The Underwater Welder are some of the best self-contained graphic novels I’ve read in some time. He’s a big fan of David Lynch and so am I, so when he’s in that mode, I’m there.
Warren Ellis - Trees. Goddamn, that book’s good. I thought he’d be running on empty by now, but nope. It’s as good as any of Ellis’s greats, if not better.
There a few others I’d like to put here–Inio Asano, Ron Wimberly, Chris Wright–but their most recent work is a few years old by now (in the case of Asano, it just hasn’t been translated). But I urge checking them out, particularly Asano’s Nijigahara Holograph, Wimberly’s Prince of Cats, and Wright’s Blacklung.